The present invention relates to the art of load handling using a load-elevating carrying device, and, in particular, to a means for quickly and accurately off-loading and transferring large loads using a load-elevating apparatus, such as a fork lift, having a load-discharging pushing mechanism.
The art of bulk load handling has been greatly enhanced by the use of material handling machinery, and, more particularly, by the use of load-elevating carrying devices such as lift trucks. In most warehouses, loads are carried on wooden pallets designed to be handled by lift trucks having two tines, or as they are frequently termed, two "forks." Shipment of various commodities can be accomplished more efficiently and economically, however, if the loads are not shipped on pallets but instead are carried on sheets, usually made of cardboard, plastic, etc., sometimes referred to as "slip sheets." While use of slip sheets eliminates the bulk and weight of pallets during transportation, handling loads which are stacked on slip sheets present some unique problems for the lift truck operator.
When a conventional palletized load is to be unloaded, merely lowering the forks to the proper elevation completely frees the forks from the pallet so that the forks need not touch the pallet or the load as the forks are retracted from the pallet. When a slip sheet mounted load is to be unloaded, however, the weight of the load and the increased load-supporting fork surface area provide a very substantial friction which interferes with the retraction of the forks from beneath the load. Such loads have tended to stick to the forks as the forks have been retracted, preventing proper load placement, and sometimes damaging a load.
Attempts to overcome these problems have led to development of off-loading assist mechanisms such as a comb-like attachment through which the load forks may be retracted, with the "teeth" of the comb functioning to strip or comb the load from the forks to leave the load on a pallet. See U.S. Pat. No. 3,381,834. More recently, lift trucks have been provided with a "push-pull" mechanism which clamps onto a load bearing sheet and pulls the load onto the load carrying members or platens at the front of the truck. See U.S. Pat. No. 3,604,414 and U.S. Pat. No. 4,217,074.
Even with these load-handling assist developments, off-loading a load-bearing slip sheet is a time-consuming task, especially when the load is a stack of packages which contain a breakable product. This problem is not alleviated by use of palletized loads in storage facilities, since transported loads must still be transferred to the pallets.
Specifically, when a slip-sheet load is off-loaded, initial care must be taken to properly align the load over the receiving pallet or surface. This task is exacerbated by the fact that the tips of the platens, which must be held at an appropriate angle of from about 3.degree. to 4.degree. by tilting the mast of the lift, are generally positioned slightly above the receiving surface while the push-pull mechanism pushes the load from the platens. This process can easily lead to misalignment such as side slippage or over-drop.
Furthermore, as the load is discharged from the platens, the lift vehicle must be made to move simultaneously in the opposite direction in order to maintain alignment of the edges of the discharging load and the receiving surface. Further maneuvers, such as stopping the vehicle and lowering the platens, are also required during discharge to compensate for upward deflection of the platens resulting from the reduction in weight. Time and care are required to perform this tedious off-loading or load transfer process which causes it to be quite inefficient. Moreover, the lift operator's patience and diligence are quickly eroded normally resulting in damage to the product.
It is, therefore, an object of the present invention to provide, among other things, a means for discharging loads from a load-elevating carrying vehicle having a load-discharging push mechanism whereby the problems usually associated with off-loading are overcome.